The present invention relates in general to fuel injection systems and devices for internal combustion engines. More specifically tile present invention relates to an improved mechanical design for portions of a fuel injection device so as to provide a more reliable, lower cost fuel injector.
Many motor vehicles, whether compression ignition or spark ignition engines, are provided with electronic fuel injection systems in order to satisfy the need for precise and reliable fuel delivery into the cylinders of the engines. Precision and reliability are demanded to address the goals of increasing fuel efficiency, maximizing power output, and controlling undesirable products of combustion.
Several electronic fuel injection systems designed for internal combustion engines use a mechanical linkage from the engine in order to pressurize the fuel charge. Using mechanical pressurization, an extremely high injection pressure, now often exceeding 20,000 psi (13,800 Newtons per square centimeter) and occasionally reaching a transient peak value of 23,500 psi (16,200 Newtons per square centimeter), is developed within the timing chamber of the injector. A higher fuel injection pressure provides a cleaner exhaust because particulate emissions are reduced, and is thus desirable to meet the tightened emissions standards which are being and will be imposed on motor vehicles.
One feature of the electronic fuel injection system which can be regarded as the predecessor to the present invention is the addition of a solenoid control valve to the top area of the injector. The predecessor injector, as well as the fuel injection device of the present invention, uses cam shaft actuation in order to build injection pressures. While much of the operation of the fuel injection device of the present invention is virtually identical to the predecessor design, certain improvements have been made in order to improve the quality and to lower the cost. The number of parts has been reduced and a plurality of high pressure seal joints have been eliminated. The reduction in the trapped volume, a consequence of the present invention, improves performance of the fuel injection device of the present invention over that of the predecessor design.
In addition to the predecessor injector which has been mentioned above and which is described in greater detail hereinafter, there are a wide variety of other fuel injection systems and devices. A representative sampling of these other systems and devices is provided by the following listing:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,281,792 Sisson et al. Aug. 4, 1981 4,398,670 Hofmann Aug. 16, 1983 4,410,137 Perr Oct. 18, 1983 4,640,252 Nakamura et al. Feb. 3, 1987 4,903,896 Letsche et al. Feb. 27, 1990 ______________________________________
As will be apparent from the description of the present invention as set forth hereinafter, there are a number of structural differences between the present invention and the listed sampling of earlier injection devices as well as the predecessor injector design. For example, neither the predecessor design nor any of the listed references disclose a unit fuel injector having a one-piece adapter positioned between an upper body and a lower nozzle wherein the adapter includes both a needle valve spring cavity and a second cavity for receiving an injector (metering) plunger. Further, neither the predecessor design nor any of the listed references disclose the use of a stepped button or a straight button and stem combination positioned in the spring cavity for setting the lift of the injector needle.